The present invention relates to a thermosensitive recording material which is improved on the recording sensitivity and the whiteness of the background thereof.
The thermosensitive recording material according to the present invention comprises (a) a support material, (b) a plurality of undercoat layers successively overlaid on the support material, and (c) a thermosensitive recording layer formed on the undercoat layers.
A conventional thermosensitive recording material comprises a support material, for example, a sheet of ordinary paper or synthetic paper, and a thermosensitive recording layer formed on the support material. Colored images can be readily formed by image-wise application of heat. A recording apparatus for use with the thermosensitive recording material is relatively simple in mechanism and compact in size and inexpensive in maintenance. Due to such advantages of the recording apparatus and the ability to form colored images by simple application of heat, such thermosensitive recording materials are widely used for recording a variety of information.
However, conventional thermosensitive recording materials still have the shortcomings that the thermal response, that is, thermal recording sensitivity, is insufficient for high speed recording, and that the whiteness of the background of the recording materials is not high.
The inventors of the present invention discovered that the thermal recording sensitivity can be improved to some extent by interposing an undercoat layer between the support material and the thermosensitive recording layer, so that a variety of undercoat layers were proposed, for instance, as disclosed in Japanese Laid-Open Patent Applications No. 55-86789, No. 55-140590, No. 56-27394, No. 56-44687 and No. 59-225987.
It is desired that the undercoat layer interposed between the support material and the thermosensitive recording layer has at least the following three functions, (i) smoothing the surface of the support material, (ii) facilitating the smoothing of the surface of the thermosensitive recording layer when the layer is subjected to calendering, and (iii) hindering the diffusion of heat from the thermosensitive recording layer to the support material at image-wise application of heat to the recording layer, thereby attaining effective use of the applied heat and sharp image formation in the recording material.
In the thermosensitive recording materials disclosed in the above Japanese laid-open patent applications, a single undercoat layer is employed. In this case, however, it is not always easy or sometimes impossible to attain the above three functions simultaneously by the single undercoat layer, since the components necessary for attaining the three functions, when all mixed, may work so as to cancel their desired effects. Furthermore, it is difficult to make a single, uniformly thin undercoat layer when all the necessary components for attaining the three functions are contained in the single undercoat layer. When the undercoat layer does not perform the above functions, the thermosensitive recording material does not attain high thermal recording sensitivity and high whiteness of the background of the recording material.